1. Field of the Invention
The invention relates to a roll shift type rolling mill for rolling a plate by alternately, axially shifting upper and lower work rolls, and more particularly to a roll for use with such a rolling mill and a roll shift type rolling mill using such a roll.
2. Description of the Related Art
FIG. 1 schematically illustrates a conventional rolling mill for obtaining a flat-shaped plate by controlling a cross-section of a rolled plate in the widthwise direction thereof. The illustrated rolling mill is known as a roll shift type rolling mill which rolls a plate 2 by alternately, axially shifting upper and lower work rolls 1. For instance, Japanese Patent Publication No. 63-62283 has suggested such a rolling mill.
However, since the work rolls 1 of a conventional roll shift type rolling mill as aforementioned have an initial crown so that a crown control effect can be brought to all plates having a width ranging from a broad one to a narrow one, a roll crown tends to be excessive and thereby tends to cause a rolling defect. In addition, the conventional rolling mill poses another problem that, since the conventional rolling mill shifts the work rolls 1 in accordance with a width of the plate 2, a specific width makes an amount of shifting of the work rolls 1 too large, and thereby causes a vibration of the plate 2.
Thus, the inventors of the present invention have invented and filed a roll for use with a rolling mill and a roll shift type rolling mill using such a roll for avoiding a rolling defect and vibration of a plate, in order to bring a crown control effect only to a plate having a specific width.
The above mentioned roll and roll shift type rolling mill was filed in Japan on Jul. 24, 1993 as a patent application No. 5-237023. This Japanese patent application is not published yet. Accordingly, the Japanese patent application does not constitute prior art under 35 U.S.C. sections 102 or 103. It should be noted that the description of the disclosure of the application as will be made hereinbelow is only for explaining the background of the invention or for making it easy to understand the invention, and that the inventors do not thereby admit that the Japanese patent application No. 5-237023 constitutes prior art against the present invention.
As illustrated in FIG. 2, a rolling mill 10 in accordance with Japanese patent application No. 5-237023 has shift rolls 12a and 12b which can be shifted in an axial direction indicated by an arrow A. A roll barrel of each of the shift rolls 12a and 12b has a straight region 7 located at the middle thereof, sub-crown control regions 6 located at both ends thereof, and main-crown control regions 5 located between the straight region 7 and the sub-crown control regions 6. The roll barrel has an outer surface having a bus bar which is a straight line inclined to a longitudinal axis of the roll barrel in the straight region 7, having steep convex and concave curved shapes at a smaller diameter end in the main-crown control regions 5, and having gentle convex and concave curved shapes at a larger diameter end in the sub-crown control regions 6.
However, since the shift rolls 12a and 12b are formed so that they have a diameter being gradually reduced in a direction from one of the sub-crown control region to the other, there is a large difference in a roll diameter in particular at both ends of the sub-crown control region 6. Such a large difference in a roll diameter tends to cause a rolling defect and vibration of the plate. Thus, the rolling mill 10 illustrated in FIG. 2 is adapted to have an inflection line of an outer surface of the roll barrel within a maximum permissible displacement determined by a rolling defect. For instance, the maximum permissible displacement is approximately 1 mm for a roll having a length of 700 mm, and it is necessary to form the roll barrel so that the roll barrel has a gradually decreasing diameter within the maximum permissible displacement and further so that the roll barrel has various curved shapes as above mentioned. Accordingly, it is impossible for the main-crown control region to have a sufficiently steep curve. For instance, it is necessary to form such a curve in a length less than one-half, one-third or one-fourth and so on of 1 mm.
In view of the foregoing, it is an object of the present invention to provide a roll for use with a rolling mill, which has a large degree of freedom in designing a curve to be applied to an outer surface of a roll barrel, provides a large amount of crown control, and has few factors for vibrating the plate.
The rolling mill 10 illustrated in FIG. 2 can accomplish a desired crown control effect for a plate having a width equal to or smaller than a specific maximum plate width. However, in the case of rolling a plate having a width larger than the maximum plate width, there arises a problem that an irregularity is generated in plate thickness distribution at the ends of the plate. Specifically, as illustrated in FIG. 3A, when the upper shift roll 12a is shifted to the right and the lower shift roll 12b is shifted to the left (hereinbelow, such shifting is called "INC shift"), a concave crown control wherein a middle portion of a rolled plate is made concave can be accomplished. However, in such a concave crown control, there arises an irregularity wherein plate ends are formed thinner, when a plate having a width larger than specific maximum plate width is to be rolled. On the other hand, as illustrated in FIG. 3B, when the upper shift roll 12a is shifted to the left and the lower shift roll 12b is shifted to the right (hereinbelow, such shifting is called "DEC shift"), a convex crown control wherein a middle portion of a rolled plate is made convex can be accomplished. However, in such a convex crown control, there arises an irregularity wherein plate ends are formed thicker (such an irregularity is called "a quarter extension"), when a plate having a width larger than specific maximum plate width is to be rolled.
In view of the foregoing, another object of the present invention is to provide a roll shift type rolling mill which decreases irregularity in the plate thickness distribution at the ends of the plate even when a plate having a width larger than specific maximum plate width is to be rolled.